1. Field of the Invention
The present invention relates to an actuator.
2. Description of the Related Art
Recently, ion migration-type actuators utilizing ionic liquids have been developed. Ionic liquids have a feature that the potential window is wider by 1 V or more than that of electrolyte solvents containing a supporting electrolyte and a solvent, and a relatively high operating voltage of about ±3 V can be set compared with such electrolyte solvents.
Japanese Patent Laid-Open No. 2005-176428 (Patent Literature 1) discloses an ion migration-type actuator including a pair of long electrodes containing a conductive carbon material (carbon nanotubes), an ionic liquid, and an organic polymer and an intermediate layer containing an ionic liquid and an organic polymer, the intermediate layer being arranged between the pair of electrodes. In this actuator, when a potential difference is applied between two electrodes 300 and 301 (FIG. 4A) that are formed on the surfaces of an intermediate layer 200 so as to be insulated from each other, a cation 700 and an anion 600 of an ionic liquid 800 respectively migrate to an electrode 301 functioning as a cathode and an electrode 300 functioning as an anode (FIG. 4B). Consequently, an electric double layer is formed at an interface between the conductive material phase in each of the electrodes 300 and 301 and the ionic material phase. The ionic radius of the cation 700 of the ionic liquid is larger than that of the anion 600 thereof. As a result, a steric effect of the ions that migrate to the electrodes and electrostatic repulsion caused by the formation of the electric double layer collaboratively act, and thus the electrode 301 significantly extends as compared with the electrode 300. Thus, the actuator is driven by being bent and deformed in a direction in which the cathode extends more significantly than the anode. When the polarity of the electric potential is inverted, the actuator element is usually bent and deformed in the opposite direction. This actuator is driven at a maximum operating voltage of ±3V.
However, when a potential difference larger than the potential window of the ionic liquid is applied to the above actuator described in Patent Literature 1, the ionic liquid is electrochemically decomposed, resulting in degradation of the driving of the actuator. Specifically, even if a strong electric field is applied to the actuator so as to promote the migration of the ions, a potential difference larger than the potential window of the ionic liquid cannot be applied. As a result, improvement in the force generated by the actuator has been limited.